Experimental and Computational Comparison of Two Chromate-Free Corrosion Protection Coatings for Mitigating Galvanic Attack on AA7075 Coupled to Corrosion-Resistant Steel A286 and Ti-6Al-4V Available to Purchase

Overcoming galvanic corrosion, which is common in aerospace structures, is an ever-present challenge. Noble fasteners such as stainless steel and Ti-6Al-4V are often used with AA7075-T6 and AA2024-T3, inducing damage to the aluminum alloy structural components. Corrosion damage can be slowed down through the use of coatings applied to the cathode or anode in a galvanic assembly to attempt to remove one of the four galvanic corrosion requirements. This work focuses on comparing two commercially available chromate-free coatings: a sol-gel barrier coating vs. a sacrificially pigmented polymer resin coating, with respect to the robustness of their abilities to reduce galvanic corrosion with imperfections and in different environments. These two coatings were demonstrated to provide advantages in corrosion mitigation through the reduction of cathodic current supply through experimental potentiodynamic scans and finite element method modeling simulations. Both coatings tested indicated significant current density reduction (orders of magnitude) relative to the use of bare cathodic substrates. The sol-gel coating presented a better capability for decreasing the current supply but also a higher variability compared to the pigmented polymer-based coating. Imperfections in the coatings were found to lead to the same change in the predicted corrosion damage due to the same surface areas being revealed from under the coatings.